The goal of this research is to study some of the mechanical factors affecting pleural pressure as they pertain to regional lung volume distribution and pleural liquid exchange. Regional lung volume distfibution is important to understanding the factors responsible for optimal gas exchange. The factors affecting pleural liquid exchange are important to understanding the etiology and pathogenesis of pleural effusions and to the efficient lubrication of the pleural surfaces. The first part of this proposal concerns the measurement of pleural liquid pressure as a reflection of regional lung volume. The factors responsible for the vertical-pleural pressure gradient in different body positions will be examined both experimentally and theoretically. In anesthetized animals, the effect of lung inflation on the regional lung expansion in different body positions will be measured using two techniques: measurement of pleural liquid pressure using rib capsules and measurement of alveolar size through pleural windows via videomicroscopy. Pleural pressure in the zone of apposition of the diaphragm to rib cage will be measured using fib capsules. The effects of body position and acceleration on regional lung expansion will be studied with a finite element model of the lung, chest wall and abdomen. Predictions of the pleural pressure gradient will be compared to experimental results. The second part of this proposal concerns the movement of pleural liquid within and through the pleural space. Pleural liquid pressure is governed by pleural surface pressure, the result of the interaction among the lung, chest wall and gravity. Thus the vertical gradient in pleural liquid pressure is less than hydrostatic, resuking in a net downward viscous flow of pleural liquid. In the steady state pleural liquid exchange rate equals the viscous flow, which is a function of the pleural space thickness. The effect of cardiogenic motion and ventilation on the movement of pleural liquid will be measured by injecting fluorescent microspheres and fluorescent liquid into the pleural space and following the movement of the fluorescent dye via videomicroscopy. The effect of hypertension on pleural capillary filtration will be examined by measuring in spontaneously hypertensive rats (SHR) pleural micmvascular pressure by micropuncture and the filtration rate by the movement of radioactive albumin from the blood into the pleural space.